Superabsorbent Polymers Dosage Research Articles

Using superabsorbent polymer to mitigate the fast setting and high autogenous shrinkage of carbide slag and sodium silicate activated ultrafine GGBS based composites

Alkali-activated GGBS based composite is a low carbon engineering material, but limited by some unavoidable disadvantages, such as fast setting and high autogenous shrinkage. In present work, superabsorbent polymer (SAP), which was synthesized by copolymerizing acrylic acid and acrylamide, was used to control the setting time and autogenous shrinkage of carbide slag and sodium silicate activated ultrafine GGBS based composites (CSGC). Results indicated that the fast setting of CSGC was effectively controlled by the addition of SAP. The initial and final setting time were delayed by more than 30 min and 60 min respectively, which provides the possibility to ensure the on-site construction operation. Although SAP mitigated the fast setting of CSGC, it had a negligible effect on the heat release during hydration. Autogenous shrinkage was reduced by 27% when only 0.1% SAP was added, and the compensation of autogenous shrinkage became more pronounced with the increased SAP dosage. The amount of large capillary pores above 100 nm was significantly increased in CSGC incorporating high SAP dosage, which leads to a decline in compressive strength. However, the compressive strength of CSGC with low SAP dosage can match that of reference group at 28 d, due to the internal curing effect of released water from SAP.

Feasibility study on superabsorbent polymer (SAP) as internal curing agent for cement-based grouting material

The closed working condition of grouting materials leads to insufficient curing water supply during their strength development. In this work, the superabsorbent polymer (SAP) was used as the internal curing agent for grouting material. The effects of SAP content on the rheological and mechanical properties of grouting material were studied under various water-cement ratios (w/c) and curing environments. The time-dependent variation of fresh slurry's viscosity was measured by Brinell viscometer. The pore structure and micromorphology characteristics were analyzed by Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscope (SEM). The results indicate that the addition of SAP increases the viscosity of fresh slurry and decreases its fluidity, thereby improving the slurry's internal uniformity at a higher w/c. And in its actual working condition, grouting material's strength can be boosted with less than 0.3% SAP dosage. Although SAP will introduce some irregular mesoscopic pores (0.2 − 0.3 mm), the MIP data analysis proves SAP refines the microscopic pore structure of grouting materials. SEM data analysis proves SAP optimizes the microstructure of grouting material, which cured in dry environment. In general, SAP improves the internal uniformity of grouting material by absorbing excess mixing water and gradually releasing it to promote cement hydration, which improves the strength of grouting material. Hence, SAP is a practicable internal curing agent for grouting material and 0.2% is the recommended dosage.

Effect of superabsorbent polymer and Slag Cement on concrete properties

Curing is an important yet un-engineered part in construction industry. Concrete gains its major strength during the process of curing. Researchers have actively been investigating in the field of Internal curing of concrete. The addition of admixture polymers in concrete to enhance their strength by contributing to internal curing has proven to give promising results. The use of Superabsorbent Polymer (SAP) to act as a water reservoir for internal curing with different quantity namely 0.2% to 0.5% by weight of cement were studied to find change in properties of M30 concrete under consideration with two different w/c ratios of “0.37” and “0.42”. This variation of SAP dosage by weight of cement for Ordinary Portland Cement (OPC) and Portland Slag Cement (PSC) with and without water were comparatively studied. The behavior of fresh slump and compressive strength at 7th, 14th, 28th, and 90th day for OPC and PSC with varying dosage of SAP, with and without water for both 0.37 and 0.42 w/c ratio concrete has been studied. The cost analysis of water required for conventional curing of concrete and self-curing concrete showed the latter saving up to 97% water wastage and 38% cost. It was observed that beyond 0.35% SAP dosage by weight of cement, there was no significant increase in the compressive strength of concrete.

Effects of superabsorbent polymers (SAP) on the rheological behavior of cement mortars: A rheological study on performance requirements for 3D printable cementitious materials

While the potential of incorporating superabsorbent polymers (SAP) as an additive in 3D printing cementitious materials has been a subject of interest recently, little research has been conducted on the effects of SAP incorporation on the rheological properties of cement mortars and the required performance of 3D printable cementitious materials when no other additives, such as superplasticizer (SP), are present or when SAP is added up to 1.0% by weight of the binder. Accordingly, the effects of SAP on the rheological behavior of cement mortar were analyzed in this study from the perspective of the performance requirements for 3D printable material with the SAP dosage (0%, 0.5%, and 1.0% by weight of cement), SAP particle size (100–180 and 355–425 μm), and superplasticizer (SP) presence (polycarboxylate-ether) as variables. The rheological properties of cement mortars with the same initial slump flow (180 mm ± 5 mm) were measured using a vane rotational rheometer, and their conformance to the performance requirements for 3D printable cementitious materials was studied. Static yield stress, dynamic yield stress, and plastic viscosity were calculated for each specimen using measured torque data obtained from the stress growth and flow curve experiments. The ratios of static to dynamic yield stress, plastic viscosity, and thixotropic areas were analyzed from the perspective of pumpability and extrudability, whereas the yield stress evolution and structural build-up rate were analyzed from the perspective of buildability. The results demonstrated that although the rheological properties of the SAP-incorporated cement mortar with a low water–cement ratio were similar to those of the SAP-incorporated cement mortar with a high water–cement ratio when SP was incorporated, the change in rheological properties with time and shear differed. SAP incorporation promoted the structuration of the mixtures without SP that have a high water–cement ratio due to the physical effects of SAP particles, but the effect was reversed in the mixtures with SP and a low water–cement ratio due to the water migration kinetics associated with SAP. Because a low water–cement ratio with SP is commonly applied for 3D printable materials, the findings of this study indicate that the water migration kinetics of SAP critically determines the printability of cementitious materials mixed with SAP. Given that observed effects are substantial, SAP arguably has potential as a rheology modifier for 3D printable cementitious materials.

Microstructure refinement and shrinkage mitigation of alkali-activated slag paste by superabsorbent polymer

This paper investigates the effects of superabsorbent polymer (SAP) dosage, particle size, addition method, and absorption status on the properties and microstructure of alkali-activated slag (AAS) pastes. The results show that incorporating SAP can mitigate the autogenous shrinkage and short-term drying shrinkage of the AAS pastes, mainly depending on the SAP dosage and size. The release of activator can promote the geopolymerisation around the SAP particles, which improves the local micro-hardness of the pastes and reduces the amount of capillary pores. This consequently densifies the microstructure around the SAP particles and mitigates the shrinkage of the AAS pastes. The large SAP particles are found to release activator to a farther distance than the small ones, which is more effective in mitigating the autogenous shrinkage. The promoted conversion from mesopores to gel pores in the paste with large SAP is also beneficial to reducing the driving force of autogenous shrinkage. By contrast, the addition method and absorption status of SAP particles have marginal impacts on the autogenous shrinkage as the released activators travel a similar distance within the AAS pastes. Moreover, adding SAP particles increases the number of gel pores and macropores regardless of their size or absorption status, leading to an increased long-term drying shrinkage and a weakened mechanical property of the AAS paste. Overall, the findings of this study can guide the mix design and preparation of AAS materials with SAP.

Study on expansion effect and hydration characteristics of ultra-high strength cement-based grouting materials based on humidity compensation

The combination of superabsorbent polymer (SAP) and expansive agent can effectively reduce the shrinkage deformation of ultra-high strength cement-based grouting materials (UHS-CGM) in dry environment. However, there are differences in the compensation shrinkage mechanism of SAP and expansive agent, and the presence of SAP may have adverse effects on the working and mechanical properties of grouting materials. In order to evaluate the synergistic effect of SAP with different water adsorption and release characteristics and MgO expansion agent (MEA), the influence of different SAP size and dosage on the compressive strength, restrained expansion rate, internal relative humidity (IRH) and hydration characteristics of UHS-CGM containing MEA were investigated, and then the composition and content of hydration products were analyzed by TG and XRD, the microstructures were observed by SEM in this paper. The results show that SAP improved the hydration degree of UHS-CGM and the expansion efficiency of MEA, and significantly increased the restrained expansion rate of UHS-CGM under standard curing and sealed curing, while reduced the compressive strength of UHS-CGM, and the decreasing degree was aggravated with increasing size and dosage of SAP. Overall, small size SAP has better inner curing efficiency and compensates shrinkage effect.

Understanding the shrinkage behaviour of alkali-activated slag binders modified by the superabsorbent polymer

Superabsorbent polymers (SAPs) have gained attention as internal curing agents in alkali-activated slags (AAS). The absorption–desorption kinetics of SAPs in AAS pastes were monitored using X-ray computed tomography. This study examines the influence of Angular covalently crosslinked sodium polyacrylate SAPs on AAS's reaction kinetics, pore structure, and microstructure f AAS. Meanwhile, autogenous, total drying shrinkage and continuous monitoring of internal relative humidity changes were performed. The results showed that the SAPs’ desorption kinetics is crucial in influencing the efficiency to counteract the shrinkage. SAPs significantly mitigated the autogenous and total drying shrinkage up to 90% and 30%, respectively.The incorporation of the ideal content of SAPs significantly compensated for the impact of the w/b ratio AAS properties. The optimum SAPs dosage was found to be 0.6 %, which enhanced the ability to control IC water, yielding better performance in terms of shrinkage, assisting the hydration degree, and enhancing the surface quality and anti-permeability. No reaction products were detected inside the voids of SAP, and the agglomeration of SAP was observed. However, care should be taken when incorporating a high content of SAP (i.e. > 0.6 %), which can adversely affect the properties of AAS. This work confirms that IC of AAS using SAPs is a powerful mitigating strategy, particularly when traditional curing is insufficient.

Contribution of Superabsorbent Polymers to Growth and Yield of African Leafy Vegetables

Superabsorbent polymers (SAPs) have been used as water-saving materials for limited irrigation water resources in arid and semi-arid areas. The purpose of this study was to optimize SAP application dosage and irrigation intervals on the growth of African leafy vegetables (ALVs) under greenhouse conditions. A factorial experiment was conducted under greenhouse conditions to determine the optimal SAP application, dosage, and irrigation intervals for the growth and production of African leafy vegetables. Two species of African leafy vegetables were studied: cowpea (Vigna unguiculata) and African nightshade (Solanum scabrum). The experiment was performed in a randomized complete block design comprising 25 treatments: a factorial combination of five superabsorbent polymer application doses (0 g, 0.5 g, 1 g, 1.5 g, and 2 g) SAP/Kg of soil substrate and five irrigation intervals (3 days, 4 days, 5 days, 6 days, and 7 days) with three replications. Statistical analysis of the results showed that the use of SAP in irrigation can significantly promote the growth and yield of African leafy vegetables. SAP, irrigation, and their interactions significantly affected ( P < 0.005 ) the plant height, stem diameter, leaf area, number of mature leaves/plant, and dry weight of leafy vegetables. Treatment with SAP showed higher growth parameters and yield of vegetables compared to the treatments. Treatment with 1 g SAP/kg of soil substrate and 5-day irrigation interval recorded the highest plant growth and yield, with 24%, 11.7%, 11.1%, and 85.9% increase in cowpea plant height, leaf area, number of mature leaves, and dry weight/plant, respectively. The treatment with 1 g SAP/kg of soil substrate and 5-day irrigation interval was observed as the best for the optimal production of African leafy vegetables under greenhouse conditions. Hence, SAP could be a good strategy for food production within arid and semi-arid lands where water resources are scarce.

Effect of superabsorbent polymer introduction on properties of alkali-activated slag mortar

Internal curing by superabsorbent polymer (SAP) has been applied in alkali-activated slag (AAS) systems by a few previous studies with the purpose to mitigate the autogenous shrinkage. However, the effects of SAP on other properties of AAS have been rarely studied. In this paper, the workability, strength, permeability, and frost resistance of AAS mortar with synthesized SAP are investigated besides the autogenous shrinkage. Two SAP introducing ways (dry mixing and wet mixing) are considered. It is found that the flowability of AAS mortar decreases with the increase of SAP dosage regardless of the introducing way. The strength and permeability increase with the SAP dosage when it is below a certain amount depending on the mixing way. The autogenous shrinkage can be mitigated significantly by the incorporation of SAP and the mitigating effect is more pronounced by wet mixing. The frost resistance becomes better when more SAP is introduced in either way. The mechanisms behind these phenomena are explained based on the characterization results on the reaction kinetics, reaction products and pore structure of the mixtures with SAP.

RETRACTED: Shrinkage and tensile properties of ultra-high-performance engineered cementitious composites (UHP-ECC) containing superabsorbent polymers (SAP) and united expansion agent (UEA)

Ultra-high performance engineered cementitious composites (UHP-ECC) had received extensive attention in recent years in material as well as the field of structural rehabilitation and strengthening due to its excellent mechanical properties, such as high strength and high ductility. However, the high shrinkage is one of the bottlenecks limiting widespread engineering application of UHP-ECC. In this paper, superabsorbent polymers (SAP) and United expansion agent (UEA) were introduced to mitigate UHP-ECC shrinkage. And the effect of different amounts of SAP with UEA on the shrinkage and tensile properties of UHP-ECC are investigate. Results indicate that the incorporation of SAP and UEA can effectively mitigate the autogenous shrinkage, and the autogenous shrinkage decreased with the increasing SAP dosage; however, drying shrinkage had the opposite trend. The incorporation of SAP and UEA improved the tensile ductility of UHP-ECC. The inclusion of SAP reduced the fracture toughness by increasing the matrix porosity, which produced more micro-cracking sources, thus improving the multiple cracking and strain-hardening behaviors of UHP-ECC. Conversely, the incorporation of SAP decreased the fiber/matrix interaction as well as decreasing the effective number of polyethylene (PE) fibers in the cross-section, thus reducing the tensile strength. Finally, pseudo strain hardening index of each specimen was conducted to analyze the effect of SAP with UEA on the tensile properties of UHP-ECC.

Influence of Super Absorbent Polymer on Root Characteristics and Anchorage of Amorpha fruticosa on Rocky Slope

Super absorbent polymer (SAP), known as a water retention agent, has a high capacity for water absorption, which can help enhance the soil structure. This paper studied the effects of SAP dosages on the root characteristics and anchorage of Amorpha fruticosa on rock slopes. The internal relationship between root growth effect and soil was discussed, and a specific reference was provided for the rational application of SAP on slopes. Using the pull-out and tensile resistance tests, we systematically studied the changes of soil properties, root distribution, root tensile strength, and root anchorage under six different SAP dosages. The results indicated that: (1) With the increase in SAP dosage, the natural soil water content and water content after 24 h of watering increased significantly, whereas the contents of TN, TP, and TK decreased dramatically. (2) With the increase in SAP dosage, the amount and length of first-order and secondary lateral roots decreased significantly, and there was no significant difference in diameter. The amount of downslope first-order and unembedded secondary lateral roots is greater than upslope. The amount of upslope embedded secondary lateral roots is greater than in downslope. (3) Tensile strength: embedded secondary root > non-embedded secondary root > first-order lateral root; upslope root > downslope root. (4) With the increase in SAP dosage, the plant anchorage drops noticeably. This study concluded that the significant addition of SAP could enhance the tensile strength of upslope embedded secondary lateral roots but would adversely affect soil nutrients, root distribution, and root anchorage. The addition of SAP in this test had no significant effect on improving slope stability. From the perspective of reinforcement capacity, we cannot blindly pursue the survival rate and other high dosage use of water retention agents to increase the risk of slope destabilization.

Improving internal curing efficiency through adjusting ab- and desorption curve of superabsorbent polymer in cement pastes using sodium carbonate

Superabsorbent polymer (SAP) has a prominent effect on relieving autogenous shrinkage of low w/c cement-based materials. It is quite important to improve internal curing efficiency of SAP considering the concrete performance and economic cost. In this paper, proper Na2CO3 dosage by cement mass was added into cement pastes to improve internal curing efficiency of SAP. Through X-ray radiography, the ab- and desorption curves of SAP in cement pastes with different Na2CO3 dosage were characterized. Through corrugated tube method, the autogenous shrinkage curves in SAP-containing cement pastes with and without optimal Na2CO3 dosage were obtained. From the view of effective internal curing water content of SAP, internal curing efficiency of SAP with 0.2 wt% SAP dosage and optimal 0.4 wt% Na2CO3 dosage can be improved by 52.3%, compared to that without Na2CO3. From the view of autogenous shrinkage curves, to achieve same internal curing effect, 0.4 wt% SAP dosage can be approximately reduced to 0.3 wt% SAP dosage, with 25% reduction rate of SAP dosage through adding 0.4 wt% optimal Na2CO3 dosage. Further, the mechanism of improving internal curing efficiency of SAP with proper Na2CO3 dosage is revealed.

Rheological characterization of cemented paste backfills containing superabsorbent polymers (SAPs)

The addition of superabsorbent polymers (SAP) to cemented paste backfill (CPB) made from tailings slurries may offer a good alternative to the dewatering components of the conventional CPB production owing to their high-water absorption and retention capacities. Therefore, an experimental program was implemented to characterize the rheological behavior of CPB incorporating an SAP. Two types of binder comprising a general use Portland cement (GU) and a blended binder (GUSL) consisting of 80% ground granulated blast furnace slag (GGBFS) and 20% GU were used. Two different binder proportions, Bw (=100 × Mbinder/Mdry-tailings) of 4.5 and 7% were tested. An SAP dosage (ratio of the dry mass of SAP to the volume of the tailings slurry) of 30 and 34 kg/m3 was assessed in this study. Results showed that the SAP addition distinctly reduced the yield stress (τ0) and the infinite shear viscosity (μ∝) and increased the small cone (H = 150 mm) slump height (s) of such mixtures over time. Moreover, The SAP-thickened tailings CPB (SAP-TT CPB) showed a severe shear-thinning behavior marked by a negative flow index (n < 0) and moderate to extremely low yield stress (τ0 in the range 21–78 Pa), while the corresponding reference CPB without SAP added (Ref) exhibited a normal shear-thinning behavior with moderate to slightly high yield stress (τ0 in the range 76–206 Pa).

Effect of Internal Curing by Super Absorbent Polymer on the Autogenous Shrinkage of Alkali-Activated Slag Mortars.

Alkali activated slag (AAS) mortar is becoming an increasingly popular green building material because of its excellent engineering properties and low CO2 emissions, promising to replace ordinary Portland cement (OPC) mortar. However, AAS’s high shrinkage and short setting time are the important reasons to limit its wide application in engineering. This paper was conducted to investigate the effect of internal curing(IC) by super absorbent polymer (SAP) on the autogenous shrinkage of AAS mortars. For this, an experimental study was carried out to evaluate the effect of SAP dosage on the setting time, autogenous shrinkage, compressive strength, microstructure, and pore structure. The SAP were incorporated at different dosage of 0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 percent by weight of slag. The workability, physical (porosity), mechanical, and shrinkage properties of the mortars were evaluated, and a complementary study on microstructure was made. The results indicated that the setting time increased with an increase of SAP dosage due to the additional activator released by SAP. Autogenous shrinkage decreased with an increase of SAP dosage, and was mitigated completely when the dosage of SAP ≥ 0.2% wt of slag. Although IC by means of SAP reduced the compressive strength, this reduction (23% at 56 days for 0.2% SAP) was acceptable given the important role that it played on mitigating autogenous shrinkage. In the research, the 0.2% SAP dosage was the optimal content. The results can provide data and basis for practical application of AAS mortar.

Influence of SAP on the chloride penetration and corrosion behavior of steel bar in concrete

The steel corrosion induced by chloride penetration is a great threaten to concrete structures, in particular exposed to marine environments. Super absorbent polymer (SAP), as a water reservoir, is probably conducive to reinforced concrete suffered from steel corrosion in marine environments. Therefore, the influence of SAP on the chloride penetration and corrosion behavior of steel in concrete were investigated using concrete mixed with 0∼2 kg/m3 SAP. The results indicate that the permeability and chloride diffusion coefficient consistently rise up with increasing with SAP dosage. Furthermore, the higher SAP dosage results in an ascending free chloride content when subjected to tidal zone. However, when exposed to atmosphere zone, the effect of SAP can be neglected. Moreover, the corrosion current of the sample with SAP are larger than that without SAP, while more corrosion products can be observed in the sample with SAP. Since the stress and strain applied on concrete and internal steel bar of specimens with SAP are apparently smaller, the propagation of crack caused by steel corrosion is probably postponed. Thus, it can be roughly concluded that for concrete subjected to marine environment, adding SAP to concrete can delay the failure process of reinforced concrete to some extent and an optimized dosage of SAP is suggested to be 1 kg/m3.

Effect of superabsorbent polymer admixtures on hygric and thermal properties of cement mortar

Materials known as superabsorbent polymers (SAP) or hydrogels are currently used in quite a few applications, ranging from diapers or napkins to nutrient carriers and soil conditioners. The great ability of SAPs to absorb and hold a significant amount of water can be utilized well also in the construction sector. For instance, SAPs can serve as effective admixtures for mitigation of autogenous shrinkage of high-performance concrete, frost protection, or cracks sealing. In this paper, basic physical, hygric and thermal properties of cement mortars containing superabsorbent polymer admixtures are analyzed. Basic physical characteristics are measured using the water vacuum saturation method and helium pycnometry. Moisture diffusivity is determined by utilizing the results of water sorptivity measurements, water vapor diffusion permeability is measured by the cup method. Sorption isotherms are determined by the desiccator method in the range of relative humidity of 11% – 96%. Thermal conductivity and specific heat capacity are measured by pulse method. Experimental results show a very significant dependence of all hygric and thermal parameters on the SAP dosage in the mix.

Synergetic effect of MEA and SAP on the deformation and mechanical properties of concrete

This paper presents an experimental investigation on the synergetic effect of magnesium oxide expansion additive (MEA) and superabsorbent polymer (SAP) on the long-term drying shrinkage, autogenous shrinkage, internal humidity and mechanical strength of concrete. Concrete with varying dosages of MEA (0, 4, 6, 8 and 10%) and SAP dosage (0, 0·2, 0·4 and 0·8%) was studied to assess the synergetic effect of MEA and SAP on concrete. The results revealed that the long-term drying shrinkage of concrete could be effectively inhibited by a hybrid system based on SAP and MEA addition. SAP had a significant effect on maintaining the internal relative humidity of concrete. The hybrid system of 0·4% SAP and 6% MEA not only eliminated autogenous shrinkage but also controlled the deformation of expansion to a minimum. The addition of SAP and MEA generally resulted in a reduction in the cube strength of concrete. Scanning electron microscopy and stereomicroscopy results showed that larger voids were formed by desorbed SAP, which had a negative effect on the cube strength of concrete.

The Performance of Super Absorbent Polymer (SAP) Water-Retaining Asphalt Mixture.

Lowering the temperature of the road surface is one efficient way to alleviate the urban heat island effect. Therefore water-retaining asphalt mixture was produced by adding super absorbent polymer (SAP) containing cement mortar to the porous asphalt mixture. In this study, the water absorption capacity, mechanical strength and fluidity of the cured water-retaining mortar were investigated to determine the optimum SAP dosage in water-retaining mortar. Furthermore, the microstructure of the hardened water-retaining mortar was studied using scanning electron microscopy (SEM) to determine the morphology and distribution of SAP in the final product, which may help to understand the influence of SAP on water retention performance and decipher its underlying mechanism. Compared to the raw porous asphalt mixture, the water-retaining asphalt mixture showed good moisture susceptibility (retained stability (RS) ≥ 88.2%, tensile strength ratio (TSR) ≥ 81.8%), good rutting resistance (9336–10,552 times/mm) and low temperature crack resistance (3383–3621 MPa), as well as significant cooling effects (10–12 °C). The results illustrate that the prepared SAP water-retaining asphalt mixture has good potential in reducing dust and enhancing road performance.

Autogenous Healing of Early-Age Cementitious Materials Incorporating Superabsorbent Polymers Exposed to Wet/Dry Cycles.

This study experimentally investigated the autogenous healing performances of cementitious materials incorporating superabsorbent polymers (SAPs) after exposure to eight cycles of wet/dry conditions. In each cycle, cracked cement paste specimens with different SAP dosages were exposed to wet conditions for 1 h, during which capillary water absorption tests were conducted, and then exposed to dry conditions for 47 h. The test results reveal that the initial sorptivity values of the reference, 0.5% SAP, 1.0% SAP, and 1.5% SAP specimens after one cycle were decreased by 22.9%, 36.8%, 42.8%, and 46.3%, respectively, after eight cycles. X-ray micro-computed tomography analysis showed that the crack volume percentages filled with healing products were 1.1%, 1.6%, 2.2%, and 2.9% in the reference, 0.5% SAP, 1.0% SAP, and 1.5% SAP specimens, respectively. As the cycling was repeated, the reduction ratio of the initial sorptivity and the quantity of healing products were increased with increases in SAP dosage. Furthermore, more healing products were distributed near SAP voids than in other sections in the specimens. This study demonstrates that the incorporation of SAPs in cementitious materials can enhance the autogenous healing performances of materials exposed to cyclic wet/dry conditions.

Internal curing of alkali-activated fly ash-slag pastes using superabsorbent polymer

To mitigate autogenous shrinkage that may cause early-age cracking of alkali-activated fly ash-slag (AAFS) concrete, internal curing using superabsorbent polymers (SAP) is employed in this study. AAFS pastes with different SAP dosages (0–0.5%) and slag replacement ratios to fly ash (15–30%) are investigated. Experimental results indicate that with the addition of SAP workability of fresh paste is improved while compressive strength is comparatively reduced. As SAP dosage increases from 0.2% to 0.5%, chemical shrinkage and autogenous shrinkage of AAFS pastes are reduced by around 18% to 45% and 76% to 85%, respectively. Internal curing of SAP is found to lower the heat peak and shift the peak to the right. This indicates the slower hydration rate corresponding to the lower chemo-mechanical deformation (chemical shrinkage), which contributes to the mitigation of autogenous shrinkage. Therefore, internal curing by means of SAP is an efficient method for mitigating autogenous shrinkage in AAFS pastes.